Caoa and Banaji
in the Harvard Psychology Dept. introduce their study:
Imagine meeting Jonathan and Elizabeth. One person is a doctor. The other is a nurse. Who is the doctor? Or imagine that an employer is deciding to hire either Colin or Jamaal. A background check will reveal that one person has a violent felony on his record and therefore will not be hired. Who is the violent felon? Before individuating facts are learned, when only gender or race is known, one of two principles can guide beliefs.
The first, which we call the base rate principle, supports the belief that Jonathan is the doctor and Jamaal is the violent felon. If ignoring base rates is considered an error, then one must realize that doctors are more likely to be men than women and people with violent felonies on their record are more likely to be Black than White. In fact, because group membership contains useful information for deciding whether an individual has a certain attribute, stereotypes have been conceptualized as base rates. Moreover, decision theorists have shown that base rates are critical ingredients for making predictions, as neglecting base rates will cause predictions to deviate from what is statistically likely.
Using these base rates, however, is inconsistent with a second principle that we call the fairness principle. By this account, it is morally proper to assume a fair coin, so to speak. Jonathan and Elizabeth are equally likely to be the doctor and Colin and Jamaal are equally likely to have a violent felony on their record. Motivated by egalitarian values, many people believe that base rates cannot and should not be used to make such predictions. In fact, the value of fairness is deeply woven into many legal systems. American courts have rejected the use of base rates to determine guilt, and the European Union has banned gender-based insurance premiums.
In the present work, we assess which principle guides beliefs before individuating facts are learned. Given only information about gender, do beliefs favor Jonathan to be the doctor or both Jonathan and Elizabeth equally to be the doctor? We then assess if the base rate and fairness principles are set aside after individuating facts are learned. Given facts that make abundantly clear who is—and who is not—the doctor, do beliefs align with the facts?
Here is the abstract summarizing their findings:
Meet Jonathan and Elizabeth. One person is a doctor and the other is a nurse. Who is the doctor? When nothing else is known, the base rate principle favors Jonathan to be the doctor and the fairness principle favors both individuals equally. However, when individuating facts reveal who is actually the doctor, base rates and fairness become irrelevant, as the facts make the correct answer clear. In three experiments, explicit and implicit beliefs were measured before and after individuating facts were learned. These facts were either stereotypic (e.g., Jonathan is the doctor, Elizabeth is the nurse) or counterstereotypic (e.g., Elizabeth is the doctor, Jonathan is the nurse). Results showed that before individuating facts were learned, explicit beliefs followed the fairness principle, whereas implicit beliefs followed the base rate principle. After individuating facts were learned, explicit beliefs correctly aligned with stereotypic and counterstereotypic facts. Implicit beliefs, however, were immune to counterstereotypic facts and continued to follow the base rate principle. Having established the robustness and generality of these results, a fourth experiment verified that gender stereotypes played a causal role: when both individuals were male, explicit and implicit beliefs alike correctly converged with individuating facts. Taken together, these experiments demonstrate that explicit beliefs uphold fairness and incorporate obvious and relevant facts, but implicit beliefs uphold base rates and appear relatively impervious to counterstereotypic facts.
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